In general, industrial machines and construction machines have a plurality of movable parts and shaft rotation parts. The movable parts are equipped with bearings, and particularly, the shaft rotation parts are equipped with bush types of sliding bearings that are generally disposed between shafts and shaft holes and reduce frictional resistance between the shafts and the shaft holes, and lubricant is periodically supplied to the parts.
In the related art, brass-based or iron-based bearings are generally used as the bush-types of sliding bearings described above.
Recently, oilless types of sliding bearings that can reduce the frictional resistance between a shaft and a shaft hole without being frequently supplied with lubricant by manufacturing the bush types of sliding bearings in sintered bodies and then impregnating lubricant to the bush types of sliding bearings have been introduced and used as bearings that are available without an extending oil supply interval (lubrication cycle) or supplying oil.
Density of the bearings is maintained by usually dispersing a large amount of soft copper (Cu) particles on martensite made of iron (Fe), but the bearings stick to a shaft that is the counterpart made of an iron (Fe)-based alloy due to friction, when a lubrication layer breaks under a high-surface-pressure and high-temperature sliding condition.
In order to remove the problem, attempts of impregnating various types of lubricants to the bearings have been made, and as an example, it has been proposed in Korean Patent No. 0261369 to impregnate a lubricant having viscosity ranging from 260 to 950 cSt to a bearing.
However, for the bearing, too, of the related art, when the bearing is used under a high-surface-pressure and a low-speed condition, for example, when the bearing is used for a portion requiring high-surface pressure of 3 to 8 kgf/mm2 and low speed of about 1 to 5 cm/sec, as the temperature of the bearing and the periphery is rapidly increased to high temperature by frictional heat, the viscosity of the lubricant decreases, such that inter-metal contact occurs between the iron-based shaft and the iron-based bearing, which is made of the same material as the shaft, and thus frictional characteristic of the bearing decreases.
It is required to frequently supply lubricant to the bearing in order to prevent the problem, in which another problem that the lubrication cycle is reduced occurs.
As described above, the lubricant impregnated to the bearing is generally easily deteriorated under a high-temperature and high-surface-pressure condition and it is difficult to achieve smooth lubrication only with the lubricant, such that inter-metal contact necessarily occurs in this state.
Meanwhile, in inter-metal wear behavior due to the inter-metal contact, plastic deformation of the metal due to high-surface-pressure occurs, in addition to inter-metal sticking due to the high-temperature generated by friction, such that not only abnormal wear of the bearing, but abnormal wear of the shaft, which is the counterpart, are caused; therefore, the entire system of the shaft and the bearing is damaged. In particular, hardness of copper (Cu) that is soft particles dispersed on the martensite made of iron (Fe) is low and severely deformed in plastic deformation, such that wear of the bearing is accelerated.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.